1. Field of the Invention
The present invention generally relates to dental tools and equipment and more particularly to a device for removing excess mercury from dental silver amalgam and/or for mulling dental silver amalgam. Still more particularly, the present invention relates to a device that minimizes exposure to liquid and gaseous mercury by eliminating mercury contact with skin during squeezing and/or mulling and by retaining excess mercury within a sealed, properly disposable system.
2. Background of the Prior Art
Dental silver amalgam is a dental restorative material used to fill cavities in teeth. In preparing dental silver amalgam, dentist or dental assistant mixes mercury with another metal, referred to as alloy, such as silver, copper, tin and zinc. Freshly mixed, dental silver amalgam has sufficient plasticity to be condensed into a prepared cavity.
The ratio of portions of mercury to alloy mixed together vary, but basically these ratios fall into two categories. The minimal mercury to alloy ratio has essentially equal portions of mercury and alloy. When fully mixed such that each particle of alloy is coated with mercury, amalgam mixed from this ratio may be applied to cavity without further processing. In the second category, portion of mercury is greater than portion of alloy resulting in an excess mercury to alloy ratio. This excess ratio facilitates the mixing process, but requires an additional processing step immediately after mixing: the excess mercury must be expressed from resultant amalgam prior to application.
Whether excess mercury or minimal mercury to alloy is used, dental silver amalgam must be mulled after mixing. Mulling generally involves squeezing bits of amalgam mass together into a larger mass so that it can be inserted either into a dispenser or directly into a cavity.
The oldest and most common method of expressing excess mercury and mulling is for the dentist to squeeze amalgam with his fingers. To remove excess mercury, the amalgam is wrapped in a cloth or similar filtering medium that is manually squeezed to expel excess mercury. Mulling may also be accomplished by squeezing amalgam while it is wrapped in a cloth, but a more common practice had been for the dentist to place the amalgam in the palm of one hand and knead it with the fingers of his other hand.
These techniques of squeezing and mulling amalgam create a danger of mercury poisoning as well as danger of contamination of amalgam with moisture from the fingers or hand of the operator or tray on which cloth is placed. Excess mercury squeezed through the cloth cannot be easily collected either for subsequent use or proper disposal. It is common practice for the dentists or dental assistants to shake excess mercury from the cloth. As a result, the mercury ends up on the dental tray, cabinet top, floor, and in clothing and shoes of personnel. Mercury is a liquid and will run between cracks in tile, under dentist's chairs and around other equipment where it collects over a period of time. This buildup of mercury in numerous inaccessible places can create a high concentration of mercury vapor that endangers the health of all persons working in the operatory. If the floor is swept or vacuumed, mercury is dispersed. This heightens mercury vapor concentration. Mercury deposited in a waste basket may ultimately be burned in an incinerator thus contaminating atmosphere; mercury washed away in waste water contributes to pollution of water. Additionally, both squeezing and mulling result in direct skin contact with mercury. Finally, these methods result in wasting a natural resource by failing to allow for a system for reprocessing unused excess mercury. Numerous articles have noted that the present methods of squeezing and mulling result in an increased risk of mercury poisoning to the dentist and his employees. Mantyla, Protection of Dental Personnel Through Proper Mercury Hygiene, DENTAL SURVEY (June 1973) 58, 60; Cedar, Mercury Vapor: A Hazard in the Dentist's Office, DENTAL STUDENT (February 1973) 28, 30; Buchwald, Using Mercury Safely, DENTAL HYGIENE (July-August 1973) 231, 234; Buchwald, More About Mercury Hygiene, 2.
The prior art teaches numerous devices developed for the purpose of retaining excess mercury squeezed from amalgam and for limiting contact between amalgam or mercury and skin to prevent contamination of the amalgam. Other devices have been developed for the express purpose of increasing efficiency in removing excess mercury and assuring higher quality amalgam, but these devices may also retain excess mercury and limit contact between mercury and skin. None of these devices, however, has been accepted commercially. A primary difficult with these devices is that they are highly complex and costly. Examples of such highly complex devices may be found in U.S. Pat. Nos. 2,731,724, issued on the application of Nordeen (mechanically squeezes amalgam wrapped in cloth); 3,023,889, issued on the application of Barr (mixes amalgam in vibrator and centrifuges excess mercury from amalgam); 2,647,638, (vibrates excess mercury from amalgam through a screen in the end of a capsule). Other devices taught by the prior art force mercury from amalgam by operation of a plunger or plungers forced against the amalgam. Excess mercury may escape around the piston and into a reservoir, as in U.S. Pat. Nos. 3,065,543, issued on the application of McShirley, and 2,618,354, issued on the application of Lyon; or it may escape through a chamois skin against which amalgam is forced by a plunger, as in U.S. Pat. No. 2,212,116, issued on the application of Eberenz. Although plunger devices are less complex and costly than the previously discussed mechanical devices, they, too, have not been accepted in practical dentistry because they require additional time consuming steps; i.e., placing the amalgam in a small cylinder and then removing it. None of these devices provide a means for efficiently mulling amalgam. U.S. Pat. No. 2,716,816, issued on the application of Brown, teaches a device designed to minimize contact between skin and amalgam during mulling. While using the device, the dentist must wear a finger cot or the like. Furthermore, the device taught by Brown is not adapted to remove excess mercury from mulled amalgam. Because of these problems, manual manipulation remains essentially the exclusive method of removing excess mercury and mulling the amalgam.
Additionally, none of these prior art devices offer sufficient protection from mercury poisoning. Since all these devices require cleaning after use, there is a high probability of contamination of waste water. Devices requiring use of high speed amalgamators may contribute to mercury contamination by dissipating fine droplets of mercury through the air. See, Nixon and Rowbotham, Mercury Hazards Associated with High Speed Mechanical Amalgamation, 131 Brit. Dent. J. 308 (1971). Mercury contamination occurs during loading and unloading of the plunger devices and during the entire mulling process of the Brown, supra, device. It is clear therefore, in view of the health hazard imposed by regular exposure to mercury vapor, that there is a present need for a low-cost, safe, simple and easily utilized device that will allow removal of excess mercury from amalgam and mulling of amalgam during an operation while at the same time minimizing danger of mercury contamination.
It is an object of the present invention to provide a simple, low-cost device capable of mulling and removing excess mercury from amalgam while enhancing and promoting environmental protection by reducing contamination of air and water by mercury.
It is a further object of this invention to provide a device that will remove excess mercury from dental amalgam and mull amalgam during an operation that does not require the dentist to perform any tasks in addition to those presently practiced in the art.
It is a still further object of this invention to provide a device that eliminates direct skin contact with mercury or amalgam and permits direct loading of a dispenser.
It is yet still another object of this invention to promote conservation of mercury and amalgam scraps of silver, copper, tin and zinc.
It is yet a still further object of this invention to provide a device that prevents contamination of dental silver amalgam mass by moisture from fingers or hands of dentist or dental assistant, or by moisture from dental tray when device is placed on tray.